1. Field of the Invention
The present invention relates to a method of and an apparatus for mounting plate fins on hairpin pipes during assembly of heat exchanger fins.
2. Description of the Prior Art
As shown in FIG. 1 of the accompanying drawings, fins in heat exchangers have heretofore been assembled by stacking a multiplicity of plate fins a that have been punched by a fin press (not shown), inserting a multiplicity of U-shaped hairpin pipes b of copper through the stacked plate fins a, and then interconnecting the upper open ends of the hairpin pipes b with U bends c, thereby providing a continuous passage through the hairpin pipes b and the U bends c. Heat exchanger fins have typically had 36 sets of 250 through 320 plate fins a securely joined in a stacked form by the hairpin pipes b.
Each of the plate fins a is produced by punching a thin rectangular sheet of aluminum having a width of 19 mm and a length of 200 mm, for example. As illustrated in FIG. 2, nine to ten holes 1a are defined in the plate fin a and have peripheral edges raised to provide fin collars 1b and free edges bent outwardly to provide flares 1c. These holes 1a are arranged in a zigzag row, and those holes 1a which are located close to one edge of the plate fin have edges spaced from the edge of the plate fin by small distances which are 1 to 2 mm at minimum.
When the hairpin pipes b are inserted through the holes 1a in the plate fins a, the plate fins a are stacked at mutually spaced relation with the fin collars 1b serving as spacers. Each hole 1a has a diameter which is about 0.3 mm larger than the outside diameter of the hairpin pipes b. After the plate fins a have been mounted on the hairpin pipes b, both of the open ends of each hairpin pipe b are flared toward the curved end thereof in order to secure the plate fins a to the hairpin pipes b. Since the plate fins a are in the form of thin sheets, they are liable to be bent or otherwise deformed. Therefore, the plate fins a have conventionally been mounted on the hairpins b exclusively manually as it has been difficult to automatize the operation to mount the plate fins a on the hairpin pipes b. More specifically, the hairpin pipes b have been manually inserted through the holes in the plate fins a arranged in lateral alignment. The prior assembling procedure has therefore required an increased expenditure of labor and time.
According to another assembling practice, plate fins which have been punched by a fin press are temporarily stacked on a stacker, and then picked up and arranged in mutual alignment so that a few or all hairpins can be inserted through the plate fins in a separate assembling step. This prior assembling procedure, however, is disadvantageous in that it is difficult to pick up a variety of different types of plate fins, and a mechanism for aligning the picked-up plate fins is quite complex in construction.